1. Field of the Invention
The present invention generally relates to a portable GPS type distance/speed measuring apparatus. More specifically, the present invention is directed to a portable distance/speed meter capable of calculating/displaying both a travel distance and a travel speed based upon positioning data acquired by receiving GPS electromagnetic waves. Furthermore, the present invention is related to such a portable type distance/speed meter suitable for measuring a travel distance and a travel speed when a person having this portable meter who walks, or runs, while selectively using the Doppler speed measuring method.
2. Description of the Related Art
In the GPS (Global Positioning System), 24 sets of the GPS satellites orbit on 6 sets of orbit courses located at an inclined angle of 55 degrees at a distance of approximately 20,200 km on the earth, and travels for approximately 12 hours per one turn. While navigation data required for positioning, transmitted from more than 3 GPS satellites under the most receivable condition are received by a GPS receiver, positioning calculations are carried out by measuring propagation delay time of these navigation data so as to determine travel direction/present position of a user.
In this GPS, two different frequencies xe2x80x9cL1 (=1.57542 GHz)xe2x80x9d and xe2x80x9cL2 (=1.22760 GHz)xe2x80x9d are prepared for the transmission frequencies of the GPS satellites. Since the C/A code (namely commercial-purpose, code being free-opened) is transmitted at the frequency of 1.57542 GHz (equal to GPS transmission frequency xe2x80x9cL1xe2x80x9d) one GPS transmission frequency xe2x80x9cL1xe2x80x9d is utilized in general-purpose positioning operation. It should be understood that the GPS signal having this frequency xe2x80x9cL1xe2x80x9d is modulated in the PSK (Phase Shift Keying) modulating method by using the pseudonoise code, and then the PSK-modulated GPS signal is transmitted by way of the spread spectrum communication system. This pseudonoise code corresponds to the synthesized wave made from the C/A code used to discriminate the desirable GPS satellite from all of the GPS satellites, and also the navigation data such as the GPS satellite orbit, the GPS satellite orbit information,, and the time information.
FIG. 6 is a schematic block diagram representing an arrangement of a GPS receiver 200 capable of receiving a GPS electromagnetic wave (namely, GPS signal having frequency of xe2x80x9cL1 (=1.57542 GHz)xe2x80x9d) transmitted from a GPS satellite. As shown in FIG. 6, the GPS receiver 200 is arranged by a reception antenna 201, an L-band amplifying circuit 202, a down-converter circuit 203, a voltage comparing circuit 204, a message decrypting circuit 205, and a positioning calculating circuit 206. The reception antenna 201 receives GPS electromagnetic waves transmitted from the GPS satellites. The L-band amplifying circuit 202 amplifies a GPS signal having an L-band frequency among the received GPS signals. The down-converter circuit 203 performs a down converting operation of the amplified GPS signal by multiplying this received GPS signal by a signal produced from a local oscillating circuit 107. The voltage comparing circuit 204 digitally converts the GPS signal down-converted by the down-converter circuit 203 into a digital GPS signal. In the message decrypting circuit 205, the digital GPS signal inputted from the voltage comparing circuit 204 is multiplied by a C/A code generated from a C/A code generating circuit 208 so as to acquire both navigation data and carrier wave phase information corresponding to a pseudodistance. The positioning calculating circuit 206 calculates positioning data by using both the navigation data and the carrier wave phase information, which are entered from the message decrypting circuit 205. It should also be noted that the local oscillating circuit 107 corresponds to such a circuit capable of producing a signal used to convert a received GPS signal into another signal having a desirable frequency.
Next, reception operation of this GPS receiver 200 will now be described. In FIG. 6, the L-band amplifying circuit 202 selectively first amplifies the GPS signal having the frequency of 1.57542 GHz received by the reception antenna 201. The GPS signal amplified in the L-band amplifying circuit 202 is entered into the down-converter circuit 203. This down-converter circuit 203 converts this entered GPS signal into a first IF (intermediate frequency) signal having a frequency of from several tens of MHz to 200 MHz by using the local oscillation signal produced from the local oscillating circuit 107, and furthermore, converts this first IF signal into a second IF signal having a frequency on the order of from 2 MHz to 5 MHz. Then, the voltage comparing circuit 204 enters thereinto this second IF signal so as to digitally convert the second IF signal into the digital GPS signal by employing a clock signal having a frequency several times higher than the frequency of this entered second IF signal. In this circuit, this digitally-converted GPS signal will constitute spectrum-spread data (digital signal).
This spectrum-spread data outputted from the voltage comparing circuit 204 is entered into the message decrypting circuit 205. Then, this message decrypting circuit 205 reverse-spreads the C/A code produced from the C/A code generating circuit 208 to the entered digital signal so as to acquire both the navigation data and the carrier wave phase information corresponding to the pseudodistance. The C/A code implies the pseudonoise code identical to that of the GPS satellite.
The above-explained reception operation is carried out with respect to the respective GPS satellites in this GPS receiver 200. Normally, the message decrypting circuit 205 of the GPS receiver 200 may acquire the navigation data and also the carrier wave phase information of 4 sets of the GPS satellites, and then the positioning calculating circuit 206 acquires the positioning data (speed, present position, time information etc.) based upon the acquired navigation data/carrier wave phase information. The positioning data acquired by the positioning calculating circuit 206 is outputted to a CPU (not shown) for controlling the overall reception operation of this GPS receiver 200, or externally outputted as a digital signal.
As the method for calculating the travel distance of the main body of this GPS receiver 200 and the travel speed thereof by using the positioning data calculated by this positioning calculating circuit 206, there are known two typical calculating methods, namely the positional change calculating method and the Doppler speed calculating method. First, in this positional change calculating method, altitude/longitude information is acquired at two separate positions used to define a travel distance, and then the above-explained travel distance is calculated based upon a difference (subtraction) between two sets of the acquired altitude/longitude information. Thereafter, this calculated travel distance is divided by travel time measured by traveling the GPS receiver 200 over these two positions to thereby calculate a travel speed. However, this positional change calculating method has the following problem. That is, a so-called xe2x80x9cpositional jumpxe2x80x9d happens to occur due to the below-mentioned reasons, so that large errors are involved in the calculated travel distance as well as travel speed. Namely, the measuring precision of the positional information calculated from the normally-utilized GPS electromagnetic waves is not so high, and this positional information is likely to be adversely influenced by SA (Selective Availability) corresponding to one of the GPS positioning error factors.
On the other hand, in the Doppler speed calculating method, since the Doppler shift frequency is acquired from the positioning data, a relative speed is firstly calculated between each of the GPS satellites and the main body of the GPS receiver 200. Subsequently, a travel speed of the main body of this GPS receiver is calculated based on a difference between this calculated relative speed and a speed of each of these GPS satellites (especially, satellite speed along the direction of the GPS receiver 200) which is obtained from the navigation data (orbit information etc.) acquired in the message decrypting circuit 205. Thereafter, a travel distance of this main body of the GPS receiver 200 is calculated by multiplying this travel speed by the travel time. However, this Doppler speed calculating method has the following problem. That is, when the actual travel speed of the main body of this GPS receiver 200 is lowered, it is hard to immediately specify the travel direction of this GPS receiver 200. As a result, the ratio of the measuring error contained in the Doppler shift frequency is increased, so that large errors are also involved in the travel distance and the travel speed, which are finally calculated.
The GPS receiver with such an arrangement is described in, for instance, Japanese Patent Application Laid-Open No. Hei 8-36042 entitled xe2x80x9cGPS RECEIVER AND SPEED DETERMINING MEANS USED THEREINxe2x80x9d. Concretely speaking, this GPS receiver is provided with the speed calculating unit (corresponding to means for performing the above-described Doppler speed calculating method), and the travel speed calculating unit (corresponding to means for performing the above-explained positional change calculating method). The speed calculating unit measures the Doppler shift frequencies of the plural satellites and then calculates the speed of the GPS receiver based upon the simultaneous equations. The travel speed calculating unit calculates the speed from the travel amount of the positioning result. In response to the speed of the GPS receiver, a selection is made of any one of the speed calculating unit and the travel speed calculating unit to calculate the speed. Also, the speed calculated from the speed calculating unit is corrected by employing the speed calculated from the travel speed calculating unit.
In the above-described xe2x80x9cGPS RECEIVER AND SPEED DETERMINING MEANS USED THEREINxe2x80x9d, the Doppler speed calculating method and the positional change calculating method are selectively used so as to calculate the travel speed. However, since these calculating methods are properly selected based on the speed change, in such a case that a large error is involved in the speed itself (namely, judgement subject for speed change), the reliability of this selecting operation itself is lowered, the object such that the speed can be measured with high precision can not be achieved.
On the other hand, the above-explained GPS receivers are increasingly realized in the forms of such portable type distance/speed meters capable of measuring travel speeds/travel distances of persons, since these GPS receivers may be supplied as a digital ASIC (Application Specific IC) due to current technical progress in semiconductor fields. In the case that the above-described GPS receiver 200 is mounted on this portable type distance/speed meter, since a person walks, or runs at a relatively slow speed, it is preferable to employ the above-explained positional change calculating method as the speed calculating method thereof. However, in this case, there is a problem in the measuring error caused by the so-called xe2x80x9cpositional jumpxe2x80x9d.
Furthermore, there are many possibilities that the above-explained GPS receiver 200 cannot receive the GPS electromagnetic waves, because the reception of these GPS electromagnetic waves is disturbed by various disturbing objects, d for example, bottom places among buildings and places inside tunnels, and/or when one GPS satellite captured by this GPS receiver 200 is switched to another GPS satellite. As a result, the GPS receiver 200 can hardly acquire the positioning data, which may cause another problem in addition to the above-explained problem related to the travel speed calculation aspect. Under such an unreceivable condition of the GPS electromagnetic waves, apparently both travel speeds and travel distances cannot be correctly acquired. This fact may cause a further problem in such a case that an average travel speed is calculated in the above-described portable type distance/speed meter. In other words, since the incorrect travel speed is involved in the calculation stage of such an average travel speed, the resulting average travel speed containing a large error is indicated to the user, and furthermore, the calculation results of the correct travel speed cannot be usefully reflected onto this calculation result of the average travel speed.
The present invention has been made to solve the above-explained conventional problems, and therefore, has an object to provide a portable type distance/speed meter capable of calculating a correct average travel speed in response to various reception conditions of GPS electromagnetic waves, and suitable for measurements of a travel distance and a travel speed when a user who uses this portable type distance/speed meter walks, or runs.
FIG. 1 is a principle diagram representing an overall arrangement of a portable type distance/speed meter according to a first aspect of the present invention. That is, to achieve the above-described objects, the portable type distance/speed meter shown in FIG. 1, according to the present invention, is comprised of: a GPS (Global Positioning System) receiver 10 for receiving GPS electromagnetic waves transmitted from GPS satellites to acquire positioning data from the received GPS electromagnetic waves; a first distance calculating means 11 for calculating a travel distance of a user as a first distance based upon a difference between positional information contained in the positioning data which are acquired at two positions; a timer means 13 for measuring travel time of the user over the first distance; a first speed calculating means 12 for calculating a travel speed of the user as a first speed based upon both the first distance calculated by the first distance calculating means 11 and the travel time measured by the timer means 13; an abnormal value detecting means 14 for detecting an abnormal value of the first speed calculated by the first speed calculating means 12; an average speed calculating means 16 for calculating an average travel speed of the user based upon the first speed calculated by the first speed calculating means 12 in the case that the abnormal value of the first speed is not detected by the abnormal value detecting means 14; and a distance accumulating means 15 for accumulating the first distance calculated by the first distance calculating means 11 so as to calculate an accumulated distance in the case that the abnormal value of the first speed is not detected by the abnormal value detecting means 14. Also, in addition to the above-described arrangement, the portable type distance/speed meter of the first aspect may be arranged by employing a display means 22 for displaying the average travel speed of the user calculated by the average speed calculating means 16 and the accumulated distance calculated by the distance accumulating means 15.
As a consequence, in accordance with the present invention, the travel distance and the travel speed of the user are calculated by way of the positional change calculating method in response to the GPS electromagnetic waves acquired by the GPS receiver 10. Only when the abnormal value detecting means 14 judges that the calculated travel speed is not such an abnormal travel speed, both the average travel speed and the accumulated distance are calculated by employing this travel speed and also this travel distance. As a consequence, in such a case that either a so-called xe2x80x9cpositional jumpxe2x80x9d or an unreceivable condition happens to occur while receiving the GPS electromagnetic waves, this abnormal travel speed and the travel distance corresponding to this abnormal travel speed can be excluded from the subject GPS data used to accumulate the travel distances and also to calculate the average travel speed.
Furthermore, FIG. 2 is a principle diagram indicating an entire arrangement of a portable type distance/speed meter according to a second aspect of the present invention. In FIG. 2, the portable type distance/speed meter of the second aspect is basically comprised of: the GPS receiver 10, the first distance calculating means 11, the first speed calculating means 12, and the abnormal value detecting means 14, as represented in FIG. 1. This portable type distance/speed meter of the second aspect is further comprised of: a second speed calculating means 19 for calculating a travel speed of the user as a second speed based upon Doppler shift frequency information contained in the positioning data acquired from the GPS receiver 10; a timer means 13 for measuring both travel time of the user over the first distance calculated by the first distance calculating means 11 and travel time of the user over the second speed calculated by the second speed calculating means 19; a second distance calculating means 20 for calculating a travel distance of the user as a second distance based upon both the second speed calculated by the second speed calculating means 19 and the travel time measured by the timer means 13; a speed selecting means 17 for selecting the first speed when the abnormal value of the first speed is not detected by the abnormal value detecting means 14, and for selecting the second speed when the abnormal value of the first speed is detected by said abnormal value detecting means 14; a distance selecting means 18 for selecting the first distance when the abnormal value of the first speed is not detected by the abnormal value detecting means 14, and for selecting the second distance when the abnormal value of the first speed is detected by the abnormal value detecting means 14; an average speed calculating means 16 for calculating an average travel speed of the user by employing any one of the first speed and the second speed selected by the speed selecting means 17; and a distance accumulating means 15 for calculating an accumulated distance by employing any one of the first distance and the second distance selected by the distance selecting means 18. Also, in addition to the above-described arrangement, the portable type distance/speed meter of the second aspect may be arranged by employing a display means 22 for displaying the average travel speed of the user calculated by the average speed calculating means 16 and the accumulated distance calculated by the distance accumulating means 15.
In accordance with the present invention, both the first distance and the first speed are calculated based upon the GPS electromagnetic waves transmitted from the GPS receiver 10 by way of the positional change calculating method, and furthermore, both the second distance and the second speed are calculated based on these GPS electromagnetic waves by way of the Doppler speed calculating method. In such a case that the abnormal value detecting means 14 judges that the calculated first speed is not the abnormal travel speed value, both the average travel speed and the accumulated distance of the user are calculated by employing the first distance and the first speed. To the contrary, when the abnormal value detecting means 14 judges that the calculated first speed is the abnormal travel speed value, both the average travel speed and the accumulated distance of the user are calculated by employing both the second distance and the second speed. As a result, in such a case that a so-called xe2x80x9cpositional jumpxe2x80x9d caused by the positional change calculating method happens to occur, the Doppler speed calculating method is employed so that this portable type distance/speed meter can continuously perform the precise GPS positioning operation.
Also, according to a third aspect of the present invention, there is provided a portable type distance/speed meter in which, in the portable type distance/speed meter according to the first aspect, or the second aspect, the abnormal value detecting means 14 can compare a present speed value of the first speed with a preceding speed value thereof, which are calculated by the first speed calculating means 12, and detect the first speed as the abnormal value in the case that the first speed corresponding to the present speed value is varied at a variation rate equal to or higher than a preselected variation rate with respect to the first speed corresponding to the preceding speed value.